T Maassen From Democritus to Millikan

Democritus - 429 BC

101

First person to think of an atom. Thought the atom was a circle

Aristotle - 400 BC

102

Believed that Democritus was wrong and that all matter was made up of one of the four elements. Fire, Earth, Air, and Water.

Sir Isaac Newton

Oct 31, 1704

Believed that everything everything was mad up of atoms.

John Dalton

Oct 31, 1803

Came up with his own atomic theory.
All matter is made up of atoms.
Atoms cannot be made or destroyed. -False
Elements contain the same type of atoms. -False
Different elements contain different atoms.
Chemical reactions occur when atoms are rearranged.
Compounds are made up of two different elements.

Henri Becquerel

Oct 31, 1896

Was the first one to discover radioactivity.

Joseph John Thomson

Oct 31, 1897

Was the first man to discover electrons. Came up with the Plum Pudding Model. This model said that atoms were pools of plums (protons) floating in a pool of pudding (electrons).

Robert Millikan

Oct 31, 1908

Measured the charge and mass of an electron.

Ernest Rutherford

Oct 31, 1911

Discovered that atoms had a nucleus using his Gold Foil Experiment.

Neals Bohr

Oct 31, 1913

Created the Bohr model, which closely resembles the way the atom is depicted today.

Frances Aston

Oct 31, 1920

Discovered isotopes.

Erwin Shrodinger

Oct 31, 1926

Found that atoms consist of a nucleus and shells. Proved Bohr model incorrect. Created formula for finding where electrons are.

James Chadwick

Oct 31, 1932

Discovered the Neutron.